U.S. patent number 10,695,710 [Application Number 16/052,937] was granted by the patent office on 2020-06-30 for methods for producing ozone and oxygen mixtures.
This patent grant is currently assigned to Messer Industries USA, Inc.. The grantee listed for this patent is Messer Industries USA, Inc.. Invention is credited to Steven Finley, Frank R. Fitch, Ravi Subramanian.
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United States Patent |
10,695,710 |
Finley , et al. |
June 30, 2020 |
Methods for producing ozone and oxygen mixtures
Abstract
A method for the continuous production of ozone and recovery of
oxygen in a purge cycle adsorption process having four adsorbent
beds. The method has the steps of feeding a mixture of ozone and
oxygen to a first and second adsorbent bed wherein the first and
the second adsorbent bed adsorb ozone and allow oxygen to pass
through; recovering the oxygen from the first bed; feeding the
oxygen from the second bed to a fourth adsorbent bed, wherein ozone
is desorbed from the fourth bed; feeding clean dry air through a
valve to the third adsorbent bed, and measuring the flow rate of
the clean dry air through the valve, comparing this flow rate to a
pre-calculated value and adjusting the flow rate of the clean dry
air to equal the pre-calculated value; desorbing ozone from the
third bed; and recovering ozone from the third bed and the fourth
bed.
Inventors: |
Finley; Steven (Wayne, NJ),
Fitch; Frank R. (Bedminster, NJ), Subramanian; Ravi
(Bridgewater, NJ) |
Applicant: |
Name |
City |
State |
Country |
Type |
Messer Industries USA, Inc. |
Bridgewater |
NJ |
US |
|
|
Assignee: |
Messer Industries USA, Inc.
(Wilmington, DE)
|
Family
ID: |
69227343 |
Appl.
No.: |
16/052,937 |
Filed: |
August 2, 2018 |
Prior Publication Data
|
|
|
|
Document
Identifier |
Publication Date |
|
US 20200038801 A1 |
Feb 6, 2020 |
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B01D
53/047 (20130101); B01D 53/0454 (20130101); B01D
53/0446 (20130101); C01B 13/0259 (20130101); C01B
13/10 (20130101); B01D 53/0423 (20130101); B01D
2256/14 (20130101); B01D 2257/104 (20130101); B01D
2259/404 (20130101); B01D 2259/40007 (20130101); B01D
2259/40086 (20130101); B01D 2259/40045 (20130101); B01D
2259/40056 (20130101) |
Current International
Class: |
B01D
53/04 (20060101); C01B 13/10 (20060101) |
Field of
Search: |
;95/23,96-98,138,148
;423/219 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Lawrence, Jr.; Frank M
Attorney, Agent or Firm: Cohen; Joshua L.
Claims
Having thus described the invention, what we claim is:
1. A method for the continuous production of ozone and recovery of
oxygen in a purge cycle adsorption process having four adsorbent
beds, comprising the steps of: a) Feeding a mixture of ozone and
oxygen to a first adsorbent bed and a second adsorbent bed, wherein
the first adsorbent bed and the second adsorbent bed adsorb ozone
and allow oxygen to pass through; and b) Feeding clean dry air from
a source of clean dry air through a valve to a third adsorbent bed
and a fourth adsorbent bed and measuring the flow rate of the clean
dry air through the valve, comparing this flow rate to a
pre-calculated value and adjusting the flow rate of the clean dry
air to equal the pre-calculated value; and c) Desorbing ozone from
the third adsorbent bed and the fourth adsorbent bed, and
recovering the desorbed ozone.
2. The method as claimed in claim 1 wherein the valve provides
adjustable flow control.
3. The method as claimed in claim 1 wherein the ozone recovered is
a mixture of ozone and clean dry air.
4. The method as claimed in claim 1 wherein a flowmeter measures
flow into and out of the adsorbent beds.
5. The method as claimed in claim 1 wherein the comparing is
performed in a programmable logic controller.
6. The method as claimed in claim 1 wherein the flow rates of the
feeds are different.
7. The method as claimed in claim 1 wherein the adjusting of the
flow rate is by opening or closing the valve.
8. The method as claimed in claim 1 wherein the adsorption process
comprises cycles of five minutes or less in time.
9. The method as claimed in claim 5 wherein the valve is in
electronic communication with the programmable logic
controller.
10. The method as claimed in claim 9 wherein the valve responds in
less than one second to the electronic communication with the
programmable logic controller.
11. A method for the continuous production of ozone and recovery of
oxygen in a purge cycle adsorption process having four adsorbent
beds, comprising the steps of: a) Feeding a mixture of ozone and
oxygen to a first adsorbent bed and a second adsorbent bed wherein
the first adsorbent bed and the adsorbent second bed adsorb ozone
and allow oxygen to pass through; b) Recovering the oxygen from the
first adsorbent bed; c) Feeding the oxygen from the second
adsorbent bed to a fourth adsorbent bed, wherein ozone is desorbed
from the fourth adsorbent bed; d) Feeding clean dry air from a
source of clean dry air through a valve to a third adsorbent bed,
and measuring the flow rate of the clean dry air through the valve,
comparing this flow rate to a pre-calculated value and adjusting
the flow rate of the clean dry air to equal the pre-calculated
value; e) Desorbing ozone from the third adsorbent bed; and f)
Recovering ozone from the third adsorbent bed and the fourth
adsorbent bed.
12. The method as claimed in claim 11 wherein the valve provides
adjustable flow control.
13. The method as claimed in claim 11 wherein the ozone recovered
is a mixture of ozone and clean dry air.
14. The method as claimed in claim 11 wherein a flowmeter measures
flow into and out of the adsorbent beds.
15. The method as claimed in claim 11 wherein the comparing is
performed in a programmable logic controller.
16. The method as claimed in claim 11 wherein the flow rates of the
feeds are different.
17. The method as claimed in claim 11 wherein the adjusting of the
flow rate is by opening or closing the valve.
18. The method as claimed in claim 11 wherein the adsorption
process comprises cycles of five minutes or less in time.
19. The method as claimed in claim 15 wherein the valve is in
electronic communication with the programmable logic
controller.
20. The method as claimed in claim 11 wherein the valve responds in
less than one second to the electronic communication with the
programmable logic controller.
21. The method as claimed in claim 11 wherein the flow of clean dry
air is proportional to a total flow through the adsorbent beds.
22. The method as claimed in claim 21 wherein the proportion is
adjustable.
23. The method as claimed in claim 22 wherein the adjustment is
made through a programmable logic controller.
Description
BACKGROUND OF THE INVENTION
Ozone is utilized in a number of industrial processes, including
drinking water and waste water treatment and disinfection, pulp
bleaching, ozonolysis reactions in fine chemical production, and
flue-gas denitrification.
Ozone is an unstable compound that decomposes to oxygen under
ambient conditions and therefore it is not feasible to manufacture,
transport or store in the manner used for many chemicals supplied
through normal commerce. Rather, ozone must be produced at the
point-of-use and at the time it is needed. Since ozone is a toxic
material, it is generated only where and when it is required, in
order to limit the possibility and potential impact of
incidents.
Ozone is typically generated from oxygen utilizing a corona
discharge. Oxygen is often used as the oxygen source for ozone
generation and results in ozone concentrations of 10 to 15% by
weight (balance oxygen) being produced. Air may also be used as the
source of oxygen and produces ozone concentrations of 1.5 to 3%
(balance air). For moderate to large ozone requirements, the total
capital plus operating costs are typically less when oxygen is used
as the oxygen source.
Ozone is often utilized at 10 weight % ozone with the balance being
largely oxygen. It has been recognized that the re-use of the
oxygen from the ozone/oxygen mixture generated by oxygen-based
ozone generators can substantially improve the economics for ozone
generation.
Adsorption systems such as those marketed as OZORA.TM. by Linde AG
can be subject to severe perturbations resulting from changes in
mode and where desorbing gas can originate from two or more
sources. The OZORA.TM. system is a four bed adsorption system
designed to recover oxygen from mixtures of ozone and oxygen
streams. The adsorbent is selected to preferentially adsorb ozone,
while allowing oxygen to pass through the adsorbent. The oxygen is
either re-used by recycling it back to the inlet of the ozone
generator or is used to rinse impurities from an adsorbent bed. The
OZORA.TM. oxygen recovery system is unique in that three gas
streams must be managed: ozone/oxygen, recycled oxygen and clean
dry air (CDA)/ozone product for customer use.
The OZORA.TM. system further employs a unique bed-to-bed gas
transfer, rinse step to rinse the CDA from a recently desorbed bed
and transfer it to a receiving adsorbent bed for the initial
desorption step. Prior to the present invention, the bed-to-bed
transfer of CDA was unregulated and uncontrollable. The percentage
of flow attributable to the rinse step was solely dependent on the
difference in pressure drops across the two gas paths.
For the OZORA.TM. system, the ability to regulate at least one of
the above-mentioned flow paths is critical in controlling the
proportioning of gas flow paths. The rinse step is critical in
preparing a bed for the adsorption step by flushing nitrogen from
that bed. The rinse step flushes residual nitrogen from a bed to
control the purity of the recycled oxygen. The time required for
this step is dependent on the flow rate, which is critical for a
system that uses timing cycles. The time of the rinse step is
dependent on the flow rate for that portion of flow diverted from
the oxygen recycle stream to the rinse stream.
SUMMARY OF THE INVENTION
In a first embodiment of the invention, there is disclosed a method
for the continuous production of ozone and recovery of oxygen in a
purge cycle adsorption process having four adsorbent beds,
comprising the steps of:
Feeding a mixture of ozone and oxygen to a first adsorbent bed and
a second adsorbent bed, wherein the first adsorbent bed and the
second adsorbent bed adsorb ozone and allow oxygen to pass through;
and
Feeding clean dry air from a source of clean dry air through a
valve to a third adsorbent bed and a fourth adsorbent bed and
measuring the flow rate of the clean dry air through the valve,
comparing this flow rate to a pre-calculated value and adjusting
the flow rate of the clean dry air to equal the pre-calculated
value; and
Desorbing ozone from the third adsorbent bed and the fourth
adsorbent bed, and recovering the desorbed ozone.
In a second embodiment of the invention, there is disclosed a
method for the continuous production of ozone and recovery of
oxygen in a purge cycle adsorption process having four adsorbent
beds, comprising the steps of:
Feeding a mixture of ozone and oxygen to a first adsorbent bed and
a second adsorbent bed wherein the first adsorbent bed and the
second adsorbent bed adsorb ozone and allow oxygen to pass
through;
Recovering the oxygen from the first adsorbent bed;
Feeding the oxygen from the second adsorbent bed to a fourth
adsorbent bed, wherein ozone desorbed from the fourth adsorbent
bed;
Feeding clean dry air from a source of clean dry air through a
valve to the third adsorbent bed, and measuring the flow rate of
the clean dry air through the valve, comparing this flow rate to a
pre-calculated value and adjusting the flow rate of the clean dry
air to equal the pre-calculated value;
Desorbing ozone from the third adsorbent bed; and
Recovering ozone from the third adsorbent bed and the fourth
adsorbent bed.
Typically, the valve is a globe valve; however, alternate designs
may be employed if globe valves are deemed inappropriate due to
cost or other factors. The real requirement for the valve is that
it provide the operator the ability to adjust the flow control. The
flow rate of the CDA is adjusted by the opening or closing of the
valve.
The flow of clean dry air is to one or two adsorbent beds.
The ozone that is recovered is a mixture of ozone and clean dry
air.
The flowmeter measures flow in and flow out of the adsorbent beds.
The flow rates of the feeds to the several beds is different. A
programmable logic controller is used when the comparing step is
performed. The valve is in electronic communication with the
programmable logic controller. The valve typically responds in less
than one second to the electronic communication with the
programmable logic controller.
Typically, the adsorption process comprises cycles of five minutes
or less in time.
FIG. 1 is a schematic of a separation process for the OZORA.TM.
system. This system is an absorption system for recovering oxygen
from an ozone stream. In this first mode of operation, two beds are
desorbed using a single source of CDA (stream 3); the CDA supply
from the compressor/dryer system F and open valve 6. In this first
mode, two beds, A and B are adsorbing ozone fed through line 1 and
recycling oxygen through line 2. The remaining two beds, C and D
are desorbing ozone using CDA from line 3 to produce an ozone
product 4.
In FIG. 2, a different mode of operation for the OZORA.TM. oxygen
recovery system is described. One bed, A, is adsorbing ozone
through line 1 and recycling oxygen through line 2 while two beds C
and D are desorbing and the remaining bed B is rinsing. The rinsing
step is the step where the CDA is purged from a bed using oxygen
resulting from the adsorption of ozone from the ozone/oxygen stream
1. The CDA purged from bed B in this example is transferred to a
receiving bed D through line 5 to desorb ozone previously adsorbed
by bed D. The CDA supply from the compressor/dryer system F and
open valve 6. The volumetric flow rate of stream 1 must be the same
as stream 4 for all modes of operation.
In both FIGS. 1 and 2, the stream 4 is either comprised of stream 3
plus desorbed ozone or in the case of FIG. 2, the combined flows of
stream 3 and stream 5, plus desorbed ozone.
But providing a consistent stream 4 flow rate while providing
independent control of streams 3 and 5 is a technical challenge
faced by this invention. Prior to the methods of the present
invention, the ratio of CDA sources 3 and 5 was not independently
controllable. Secondly, the flow of ozone product 4 was prone to
upset during the mode transition and fluctuated beyond the
acceptable range.
The adsorption cycle can be a pressure swing adsorption cycle.
Typically, the adsorbent in the beds can be silica gel. These types
of cycles can have cycles times of around 7 minutes with pressures
from 15 to 20 psig and temperatures in the range of 60.degree. to
100.degree. F.
The adsorbent beds can also be present in multiples of four so that
the inventive method could operate with four, eight, twelve or
sixteen total beds.
The high and low flows are portions of the full product flow. In
the inventive method, a range of flow rates, as a function of total
flow can be 50 to 100% of the total flow rate.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic of a four bed adsorption process according to
the present invention.
FIG. 2 is a schematic of an alternative schematic of a four bed
adsorption process according to the invention.
FIG. 3 is a schematic representation of calculation blocks that are
used in comparing the flow of clean dry air to the pre-calculated
value and adjusting flow rates based on this comparison.
DETAILED DESCRIPTION OF THE INVENTION
In the methods of the present invention, a flow control is added to
the CDA supply stream identified as line 3 above in FIGS. 1 and 2.
A control valve such as a globe valve can be used to regulate the
total flow of CDA, which can be distributed to one or two beds,
depending upon the mode of operation.
The adjustments that are made to the CDA flow can determine the
total ozone product flow (4). The ozone product is the mixture of
ozone and CDA produced by a process such as the OZORA.TM. oxygen
recovery system. By regulating the flow of CDA, a consistent and
accurate control of ozone product flow can be achieved while
responding to extreme perturbations that result from step changes
associated with sequencing of the system.
The first critical factor is the ozone product flow rate set point
(SP). Stream 4 is a mixture of ozone and CDA. The flow rate set
point is a function of the mass flow rate of the ozone component of
the ozone product (M) and the ozone concentration (C) of ozone in
the ozone product. The flow rate can be calculated by using the
relationship SP=M/C(K) Where: SP is ozone product (stream 4) flow
rate set point (e.g., scfm, m3/hr) M is Ozone component mass flow
rate (e.g., pounds per day (ppd), kg/hr) C is mole fraction or
concentration of ozone in the ozone product (% ozone/100) K is a
constant; dependent on engineering units
The set point (SP) is a critical control parameter. It is the set
point for the control loop that regulates the outgoing ozone
product flow rate. This flow rate must match the flow rate of ozone
entering the oxygen recovery system (stream 1). It is important to
note for purposes of the invention that the oxygen recovery system
is not a flow through system so balance of incoming and outgoing
streams must be actively controlled. The blower speed and the
regulation of CDA flow rate are the two primary means of
controlling flow rate at the inlet (Stream 1) and the outlet
(Stream 4).
Ozone entering the system (stream 1) flows through two adsorption
beds where the ozone portion (M) of the gas is adsorbed and
retained in the two beds. Referring to FIGS. 1 and 2, the stream 2
flow rate will always be less than the sum of streams 2 (and 5) due
to the retention of ozone in the adsorbent.
Concurrently, ozone is desorbed from two beds by feeding CDA
(streams 3/3 or stream 3/5) through the beds to remove adsorbed
ozone from the beds. During desorption, the outgoing (stream 4)
flow rate will always be higher than the incoming stream 3/3 or
stream 3/5 flow as ozone is added to the incoming CDA.
Successful operation of the oxygen recovery system relies on
matching the incoming (stream 1) flow rate with the outgoing
(stream 4) flow rate. The two flow rates must be identical and
stable and generally at the same ozone concentration irrespective
of the operational step or the perturbations associated with step
transitions in the adsorbent beds. Accurate and stable control of
stream 4 flow is a key benefit of this invention.
In many ozone generator systems, ozone product flow rate is not a
controlled parameter. Often it is a value that can be derived once
other parameters are known such as ozone product flow rate and
ozone concentration. Ozone as produced for example by an ozone
generator is typically comprised of ozone molecules, oxygen and
nitrogen. A common example in weight percent would be:
Oxygen: 90%
Ozone: 8%
Nitrogen: 2%
For a given temperature, pressure and volumetric flow rate, the
mass flow rate (M) of the ozone portion of the stream can be
calculated. Often, this value; along with the ozone concentration
(C) are used to regulate power to the ozone generator cells. Since
ozone generators are controlled by regulating power, mass flow rate
(M) and concentration (C) are the two critical control parameters.
Volumetric flow rate (Q) of the gas mixture is often not
regulated.
However, Q can be calculated using the following relationship:
Q=M/C(K) Q is Ozone (stream 1) flow rate (scfm, m.sup.3/hr) M is
Ozone component mass flow rate (ppd, kg/hr) C is mole fraction or
concentration of ozone component in the ozone product (% ozone) K
is a constant; dependent on engineering units
For the purposes of this invention, the value Q can be re-stated as
a calculated set point (SP1) for the incoming gas flow rate where M
is the setting for ozone production in lbs/day or kg/hr and C is
the ozone concentration (v/v). Both values are available through
the ozone generator's control system.
The set point for stream 1 can then be calculated using the
relationship: SP1=M/C(K) SP1 is Ozone (stream 1) flow rate set
point (scfm, m3/hr) M is Ozone component mass flow rate set point
(ppd, kg/hr) C is the set point for mole fraction or concentration
of ozone component (% ozone) K is a constant; dependent on
engineering units
For the oxygen recovery system of the present invention, the flow
rate of stream 1 (Q1) is regulated by the speed of a blower (P1).
The set point for the blower is the calculated set point SP1. For
purposes of this invention, the calculated value for SP1 is also
used by the control system to regulate the ozone product (stream 4)
flow rate. Two separate control loops regulate flow into and out of
the oxygen recovery system. Each requires the same set point as
calculated above; however, the process variable (flowmeter) sources
differ since one is typically installed at the inlet of the ozone
generator while the measurement for the stream 4 flow rate is
located in line 4.
For stream 1, a flow rate set point (SP1) is calculated as shown
above and the process variable (PV1) is provided using a flow meter
in the ozone generator's oxygen inlet line. The output provides a
signal to regulate the speed of the oxygen recovery system
blower.
For stream 4, the flow rate set point (SP=SP1) is also calculated
using the function shown above; however, the process variable (PV)
is provided by a second flow meter located in the ozone product
(stream 4 line). The flow rate for stream 4 must be actively
regulated to maintain mass balance between the ozone generator and
the oxygen recovery system. In this invention, mass balance is
achieved by regulating the flow rate of CDA.
The ozone product is produced during one of two desorption steps
designed into the operating sequence. At any time in the operating
sequence, two beds are adsorbing ozone and the remaining two are
desorbing ozone. As described above, the CDA used for desorption
originates either from the CDA compressor/dryer (stream 3) or from
a rinsing bed that is being purged of CDA (5).
The desorbed ozone which is combined with CDA comprises ozone
product and ozone product from two beds is always combined to make
up the total flow of ozone product (stream 4) produced by the
oxygen recovery system.
In all cases, CDA from stream 3 supplies at least one bed with CDA
for desorption. During the step illustrated in FIG. 1, all CDA
originates from the compressor/dryer (stream 3).
During the step illustrated in FIG. 2, only a portion of the CDA
originates from the compressor/dryer. The remainder is CDA
displaced from a rinsing bed (stream 5). In any step, the flow rate
of stream 4 must match the flow rate of stream 1 even during
transitions regardless of CDA sources.
It can be determined from the above that there are significant
differences in flow requirements for stream 3, depending on which
scenario (FIG. 1 or FIG. 2) is in effect. It should be noted that
it is the nature of and in fact very typical in pressure swing
technology to cycle adsorption beds through sequences comprising
discrete steps lasting less than 5 minutes each; often less than 3
minutes each or less. As a result, the flow requirements for stream
3 change abruptly every few minutes.
A flow control valve in stream 3 is added regulate the flow of CDA.
It is required to respond very quickly (within less than one
second) to position itself for either a high flow (in the case of
FIG. 1 mode) or low flow (in the case of FIG. 2 mode).
In high flow mode (FIG. 1), CDA (stream 3) flow provides 100% of
the flow through the desorbing beds and must provide enough flow
for a stream 4 flow rate equal to stream 1 flow rate. This is
measured using a flow meter in stream 4.
In low flow mode (FIG. 2) the stream 3 flow is equal to a portion
(between 0% and 100%); typically, 30 to 70% of the required stream
4 flow.
In the present invention, the stream 3 flow is regulated to
accommodate the flow requirements for each mode and to manage the
transitions between the modes and provide for a stable and accurate
stream 4 flow rate.
A flow control valve in stream 3 regulates the flow rate. The
opening in that valve's orifice (% opening), combined with the gas
properties, inlet pressure and outlet pressure determine the flow
rate through that valve. In the present invention, a method of
regulating the CDA pressure both upstream and downstream is
provided in the form of a pressure regulator to provide consistent
upstream pressure for the stream 3 control valve. It should be
noted that the control valve's inlet pressure is regulated.
Also, the pressure drop downstream is consistent to the degree that
any slight variations are expected to have negligible impact on the
flow characteristics of the control valve (6).
By these two measures, a correlation can be established between the
position of the stream 3 control valve (6) and the expected CDA
flow rate. A table or formula can be created by an operator using
design or experimental data for a given valve to calculate the
expected flow rate for a given stream 3 control valve position.
Referring to FIG. 3 below two calculation blocks (400 and 300)
which are typically programmable logic controllers (PLCs) are
identified. Block 400 calculates the flow set point for the CDA
flow control valve (7). Block 300 calculates the CDA control
valve's position (CV3) employing a PID control algorithm.
The set point for block 300 is the value calculated by block 400.
To calculate the set point (SP3), block 400 determines the oxygen
recovery system's operational mode (FIG. 1: high flow; FIG. 2: low
flow) The total required stream 4 flow rate (SP4) Is multiplied by
a factor (n) to calculate the stream 3 flow set point. The factor
(n) determines which percentage of stream 4 flow originates from
stream 3 (CDA). By deduction, the remaining flow originates from
stream 5 (CDA transferred from a rinsing bed). For the FIG. 1
process, the value of n is 1. For the FIG. 2 process, the value of
n is between 0 and 1, typically, between 0.3 and 0.7. The
calculated set point SP3 from block 400 is the set point for block
300 to control the CDA control valve 6.
Block 300 calculates the valve position for CDA control valve 6.
The critical inputs and outputs are:
Set Point (SP): SP3
Process Variable (PV): 7 (Stream 4 flow meter)
Output (CV): 6 (CDA Control valve positioner)
301: Suspend PID calculation
302: Calculated output
Block 300 is a PID (Proportional, Integral and Derivative)
algorithm (using only Proportional and Integral gains) that
calculates an output (CV) based on changes in error (SP3-PV3).
Since there are frequent perturbations resulting from transitions
from high and low flow requirements for CDA flow, interventions are
required to suspend bop calculations and position the control valve
very quickly to the newly calculated position.
Input 301 is a discrete input used to suspend control loop
calculation during brief transition periods (<3 secs). While the
control loop is suspended a calculated valve position is forced
into the output register. In response, the valve will reposition
and CDA flow (stream 3) will increase or decrease accordingly. Once
the transition period is ended, input 301 will enable block 300 to
resume calculations to update the output (CV3). The forced position
of CDA control valve (6) will result in a very small error; hence
the control loop will respond with very small corrections to the
output (CV3) resulting in very stable control of stream 4 flow.
Typically for this invention, the transition take place quickly and
the forced output is based on the known relationship between the
control valve's position and the accompanying flow rate. This
relationship as discussed is consistent when the inlet and outlet
pressures are held constant for a given gas, in this case, CDA.
Typically, control valves do not provide a linear relationship
between valve position and flow rate. Often a polynomial
relationship exists; for example: Y=Ax.sup.2+Bx+C where: Y=Gas Flow
Rate X=Valve Position (%) A, B & C are constants specific to
the valve and the engineering units.
In one case, a valve was tested with CDA at an inlet pressure of 30
psig for valve positions ranging from 5% to 40%. CDA gas flow was
measured in scfm and the following values for the constants A, B
& C were established:
A=0.04
B=0.22
C=15.7
Within a very short period of time (<1 sec) the control valve
must move to its new position. For example, a globe valve (6) will
respond quickly and predictably to serve the needs of this
invention. The override of the control loop and the subsequent
forcing of the control valve to a new position is meant only to
serve the needs of the transition.
While this invention has been described with respect to particular
embodiments thereof, it is apparent that numerous other forms and
modifications of the invention will be obvious to those skilled in
the art. The appended claims in this invention generally should be
construed to cover all such obvious forms and modifications which
are within the true spirit and scope of the invention.
* * * * *